Numerical study of violent LNG sloshing induced by realistic ship motions using level set method

In this paper, a numerical model is developed to investigate the liquid sloshing in a real sized rectangular LNG tank when the LNG carrier is travelling in sea conditions. The numerical model solves the Navier-Stokes equations and continuity equation by using a finite difference approximation in an arbitrary moving coordinate system to represent the two-dimensional tank under three-degree-of-freedom excitations. To track the violent movement of the free surface, the level set method is applied to simulate the liquid and gas phases simultaneously. The numerical model is validated by simulating four sloshing cases under various excitations and comparing the present results with the published experimental data and numerical solutions. The emphasis of this study is put on the numerical simulation of sloshing waves in the real sized LNG tank excited by the ship motions. To achieve this, the realistic motion RAOs of the ship in seas are applied directly as the external excitation to generate the sloshing waves. A parametric study regarding filling level, excitation frequency and wave amplitude is finally performed and discussed.